The goals of this project are to further develop the baboon autologous marrow transplant (AMT) model to provide a preclinical model for human AMT. This model will be used to 1) identify and enrich the progenitor cells necessary for reconstitution of hematopoiesis in vivo after autologous marrow transplantation, and 2) determine if the recombinant cytokines, IL-3, GM-CSF, and IL-l can stimulate more rapid engraftment by enriched progenitors. This approach is based on studies in which monoclonal antibodies to CD33 and CD34 antigens have been used to separate highly immature human hematopoietic progenitors from their more mature colony forming progeny. The utility of the baboon model lies in the expression on baboon marrow cells of the CD33, CD34 and other differentiation antigens found on human leukocytes. Preliminary data suggest that enriched CD34+ marrow cells can reconstitute hematopoiesis in lethally irradiated baboons. Thus, baboon AMT provides a model relevant to man in which the contribution of specific progenitor populations to hematopoietic reconstitution after marrow transplantation can be studied. Therefore, the phenotype of reconstituting progenitor cells will be determined and the effect of recombinant human hematopoietic growth factors on baboons receiving AMT from limited numbers of enriched progenitor cells will be examined.